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pnmtojbig - PNM to JBIG file converter
pnmtojbg [ options ]
[ input-file | - [ output-file ]]
Reads in a PBM or PGM format image from a file or standard input,
compresses it, and outputs the image as a JBIG bi-level image entity (BIE)
file.
JBIG is a highly effective lossless compression algorithm for bi-level
images (one bit per pixel), which is particularly suitable for scanned
document pages.
A JBIG encoded image can be stored in several resolutions
(progressive mode). These resolution layers can be stored all in one single
BIE or they can be stored in several separate BIE files. All resolution
layers except the lowest one are stored merely as differences to the next
lower resolution layer, because this requires less space than encoding
the full image completely every time. Each resolution layer has twice the
number of horizontal and vertical pixels than the next lower layer. JBIG
files can also store several bits per pixel as separate bitmap planes,
and pnmtojbig can read a PGM file and transform it into a multi-bitplane
BIE.
- -
- A single hyphen instead of an input file name will cause
pnmtojbg to read the data from standard input instead from a file.
- -q
- Encode
the image in one single resolution layer (sequential mode). This is usually
the most efficient compression method. By default, the number of resolution
layers is chosen automatically such that the lowest layer image is not
larger than 640 × 480 pixels.
- -x number
- Specify the maximal horizontal size
of the lowest resolution layer. The default is 640 pixels.
- -y number
- Specify
the maximal vertical size of the lowest resolution layer. The default is
480 pixels.
- -l number
- Select the lowest resolution layer that will be written
to the BIE. It is possible to store the various resolution layers of a
JBIG image in progressive mode into different BIEs. Options -l and -h allow
to select the resolution-layer interval that will appear in the created
BIE. The lowest resolution layer has number 0 and this is also the default
value. By default all layers will be written.
- -h number
- Select the highest
resolution layer that will be written to the BIE. By default all layers
will be written. See also option -l.
- -b
- Use binary values instead of Gray code
words in order to encode pixel values in multiple bitplanes. This option
has only an effect if the input is a PGM file and if more than one bitplane
is produced. Note that the decoder has to make the same selection but cannot
determine from the BIE, whether Gray or binary code words were used by
the encoder.
- -d number
- Specify the total number of differential resolution
layers into which the input image will be split in addition to the lowest
layer. Each additional layer reduces the size of layer 0 by 50 %. This option
overrides options -x and -y which are usually a more comfortable way of selecting
the number of resolution layers.
- -s number
- The JBIG algorithm splits each
image into a number of horizontal stripes. This option specifies that each
stripe shall have number lines in layer 0. The default value is selected
so that approximately 35 stripes will be used for the whole image.
- -m number
- Select the maximum horizontal offset of the adaptive template pixel. The
JBIG encoder uses a number of neighbour pixels in order to get statistical
a priori knowledge of the probability, whether the next pixel will be black
or white. One single pixel out of this template of context neighbor pixels
can be moved around. Especially for dithered images it can be a significant
advantage to have one neighbor pixel which has a distance large enough
to cover the period of a dither function. By default, the adaptive template
pixel can be moved up to 8 pixels away. This encoder supports up to 23 pixels,
however as decoders are only required to support at least a distance of
16 pixels by the standard, no higher value than 16 for number is recommended
in order to maintain interoperability with other JBIG implementations. The
maximal vertical offset of the adaptive template pixel is always zero.
- -t
number
- Encode only the specified number of most significant bit planes.
This option allows to reduce the depth of an input PGM file if not all
bits per pixel are needed in the output.
- -o number
- JBIG separates an image
into several horizontal stripes, resolution layers and planes, were each
plane contains one bit per pixel. One single stripe in one plane and layer
is encoded as a data unit called stripe data entity (SDE) inside the BIE.
There are 12 different possible orders in which the SDEs can be stored
inside the BIE and number selects which one shall be used. The order of
the SDEs is only relevant for applications that want to decode a JBIG file
which has not yet completely arrived from e.g. a slow network connection.
For instance some applications prefer that the outermost of the three loops
(stripes, layers, planes) is over all layers so that all data of the lowest
resolution layer is transmitted first.
The following values for number select these loop arrangements for writing
the SDEs (outermost loop first):
0 planes, layers, stripes
2 layers, planes, stripes
3 layers, stripes, planes
4 stripes, planes, layers
5 planes, stripes, layers
6 stripes, layers, planes
All loops count starting with zero, however by adding 8 to the above
order code, the layer loop can be reversed so that it counts down to zero
and then higher resolution layers will be stored before lower layers. Default
order is 3 which writes at first all planes of the first stripe and then
completes layer 0 before continuing with the next layer and so on.
- -p number
- This option allows to activate or deactivate various optional algorithms
defined in the JBIG standard. Just add the numbers of the following options
which you want to activate in order to get the number value:
4 deterministic
prediction (DPON)
8 layer 0 typical prediction (TPBON)
16 diff. layer typ. pred. (TPDON)
64 layer 0 two-line template (LRLTWO)
Except for special applications (like communication with JBIG subset
implementations) and for debugging purposes you will normally not want
to change anything here. The default is 28, which provides the best compression
result.
- -c
- The adaptive template pixel movement is determined as suggested
in annex C of the standard. By default the template change takes place directly
in the next line which is most effective. However a few conformance test
examples in the standard require the adaptive template change to be delayed
until the first line of the next stripe. This option selects this special
behavior, which is normally not required except in order to pass some conformance
test suite.
- -v
- After the BIE has been created, a few technical details of
the created file will be listed (verbose mode).
Most of the format
pnmtojbig creates is defined by the JBIG standard.
The standard, however,
does not specify which values in the BIE mean white and which mean black.
It contains a recommendation that for a single plane image zero mean
background and one mean foreground, but the Netpbm formats have no concept
of foreground and background. And the standard says nothing about values
for multiple plane BIEs.
pnmtojbig follows Markus Kuhn's implementation
of the standard in the pbmtojbg program that comes with his JBIG library:
If the BIE is a single plane BIE, zero means white and one means black.
If it is a multiple plane BIE, zero means black and the maximal value
is white.
This program implements the JBIG image coding algorithm
as specified in ISO/IEC 11544:1993 and ITU-T T.82(1993).
pnmtojbig
is based on the JBIG library by Markus Kuhn, part of his JBIG-KIT package.
The pbmtojbg program is part of the JBIG-KIT package. The most recent version
of that library and tools set is freely available on the Internet from
anonymous ftp server ftp.informatik.uni-erlangen.de in directory pub/doc/ISO/JBIG/.
pnmtojbig is part of the Netpbm package of graphics tools.
pbm(5)
,pgm(5)
,jbigtopbm(1)
If you use pnmtojbig, you are using various patents, particularly
on its arithmetic encoding method, and in all probability you do not have
a license from the patent owners to do so.
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